1. Field of the Invention
The invention relates to a method for producing nonlinear optical microcomponents in which, by means of X-ray depth lithography and micromolding techniques, a mold insert with a waveguide structure is produced as positive mold, the waveguide structure is impressed into a polymer base material by means of the mold insert and the impressed waveguide structure is then filled with optically linear material.
2. Description of the Related Art Including Information Disclosed Under 37 CFR SS1.97-1.99
Optical microcomponents are used in optical miniature circuits in which light signals can be generated, guided in a plane through waveguides and processed as well as verified. The hitherto most important substrate materials to produce integrated optical components are glass, lithium niobate and silicon. The class of the 3-5 semiconductor materials has gained great importance for the monolithic integration of passive waveguide structures and optoelectronic components.
Known from "Technisches Messen, Special issue on Sensor 91" 58 (1991) 4, pages 152-157 is a method to produce optical microcomponents in which wafers are cut off a glass rod. The subsequent photolithographic process starts with making a suitably structured primary mask on an electron-beam recorder, which mask is copied by the direct contact method on the previously metal or photosensitive resist-coated glass wafer. After development of the resist and etching out the metal coating in the open resist areas, the desired waveguide structure is present as metal mask. To generate the waveguides, the glass wafers are put into a hot, molten salt bath wherein metal ions from the melt, driven by concentration gradients, penetrate the glass surface through the mask openings, increasing the refraction index there. After removal of the mask, individual chips are sawed out of the glass wafer and their faces polished for the later fiber coupling. The refraction index maximum of waveguides thus produced is directly at the glass surface.
Shielding the guided light waves succeeds by burying the extraneous ions below the substrate surface in a second exchange step which can be taken both diffusion-controlled (thermal) and drift-controlled (field supported).
To produce a non linear optical microcomponent on the basis of lithium niobate, a lithium niobate monocrystal is produced first--as described in "Spektrum der Wissenschaft" December 1986, page 116 ff--to whose surface is applied photolithographically a thin titanium film by means of a mask in order to impart to the monocrystal the desired waveguide structure. Then the entire arrangement is heated to about 1000.degree. C. so that the titanium penetrates the outermost lithium niobate surface. The remaining titanium is etched away.
The disadvantage of these methods is that the choice of materials to produce nonlinear optical components is restricted. In particular, the combination of optically linear and optically nonlinear materials cannot be realized in the desired variety. In addition, these known methods are too costly for the mass production of nonlinear optical microcomponents.
In order to open up polymer materials for the application of waveguides in microcomponents, X-ray depth lithography was already employed in the past (see e.g. DE-PS 36 11 246). From an X-ray resist material it is possible, by means of X-ray depth lithography, to generate waveguide structures which are filled with a suitable polymer material to form waveguides. It is also possible, by means of X-ray depth lithography and electroforming, to produce mold inserts, by means of which waveguide structures can be impressed into polymer materials. These methods were hitherto used only to produce optically linear microcomponents.